1. Field of the Invention
The present invention relates to a system and method for identifying and locating an acoustic event. More particularly, but not by way of limitation, the present invention relates to a system for identifying an explosive event, such as a gunshot, at a remote location, reporting the event including a precise time of arrival to a host system, and calculating a location of the source of the event in the host system.
2. Background of the Invention
Generally speaking, there is a long felt need for a system and method to pinpoint the exact location of the source of gunfire, particularly in an urban setting. In many large cities, gun-related violence has become a plague of epidemic proportions. It is estimated that roughly 10,000 Americans die each year from gun related injuries with an estimated 200,000 non-fatal injuries. Recent events such as the so-called Suburban Sniper in the Washington D.C. area have further underscored the need to resolve this problem. Unfortunately, prior art solutions have been either inadequate or too costly to gain wide acceptance in the field.
In a typical gunshot locating system, a plurality of sensors are situated in the field, usually at fairly regular intervals along an x-y grid. Each sensor includes a microphone and, presumably, an amplifier to produce an audio signal. The audio signal is then carried by a dedicated telephone line to a central location where the sound is processed. Upon detecting a gunshot from the processed audio, relative times of arrivals at the central location are processed to determine a location of the source of the gunshot.
One such system, U.S. Pat. No. 5,973,998 issued to Showen, et al. discloses a system wherein sensors are placed at a density of roughly six to ten sensors per square mile. Showen takes advantage of a naturally occurring phenomenon known as spatial filtering to improve the accuracy and reliability over that of prior systems. While the Showen system radically reduces the sensor density compared to prior art systems, as high as 80 sensors per square mile, each sensor, nonetheless, still requires a dedicated phone line. As one can see, to effectively monitor a large metropolitan area, an outrageous number of telephone lines would be required, resulting in a substantial investment in infrastructure, not to mention large on-going costs. Such systems can often take months to install.
In addition to the large number of dedicated phone lines required by prior art systems, such systems transport audio information over comparatively long distances. The signals, as such, are subject to a number of degrading factors such as noise, crosstalk, inadvertent disconnection, and the like. Such factors may cause gunshots to go undetected. Latency in one or more communication channels will cause the system to produce and erroneous location.
Another known method for identifying the location of a gunshot relies on a special sensor having several microphones arranged in a geometric array. A radial direction can be determined by measuring the differences in arrival times at the various microphones. Unfortunately, such systems suffer from limited accuracy in the determination of the radial angle, which in turn, translates into significant errors in the positional accuracy of the source of the noise when triangulation of two or more sensors is performed. Since errors in the radial angle result in ever increasing position error as the distance from the sensor to the source increases, the reported position will be especially suspect toward the outer limits of the sensor's range.
Another type of gunshot sensor detects a gunshot and attempts to identify a particular type of weapon, or at least a class of weapon. These systems generally analyze the duration, envelope, or spectral content of a gunshot and compare the results to known samples. Combining a trustworthy identification of a weapon with the precise location of a shot fired by the weapon would be particularly useful in the early stages of a police investigation and could allow early correlation of a crime to a repeat perpetrator.
It is thus an object of the present invention to provide a system for detecting an acoustic event, such as a gunshot, identifying the acoustic event, and fixing a location of the source of the event.
It is a further object of the present invention to provide a gunshot detection system which can be deployed over a large area without incurring undue costs in infrastructure and undue recurring costs.
It is still a further object of the present invention to provide a system for fixing the location of an acoustic event with greater accuracy than has been possible with existing systems.
It is still a further object of the present invention to provide a system for fixing the location of an acoustic event that can be rapidly deployed.